I'm attempting to make a program that will simply draw a guide (consisting of two perpendicular lines) on another program's window. I tried using a form with a transparency key and TopMost set to true, but then whenever the user inadvertently clicked the guide, it would un-focus the application. This happened a lot, and was a great source of annoyance... So I did some research, and the only lead I could find was a suggestion to "Draw directly on the other application's window". I can't find anything that tells me how to do this, or if its even possible... So I need to know one of three things:
1) Is it possible?
2) How do you do it?
or 3) is there some way to make a form completely un-focusable?
The effect I'm trying to get is so that it looks like someone physically drew the line on the monitor itself.